The invention relates to an electrical machine having a stator and a rotor, with the stator having stator slots in which a stator winding with redundant and at least three-phase winding systems is laid. The invention also relates to an electrical drive which has an electrical machine such as this and has a number of converters, corresponding to the number of poles in the electrical machine, for the electrical supply to the redundant and at least three-phase winding systems in the electrical machine.
Electrical machines such as these, in particular electric motors such as asynchronous motors or synchronous motors, are required for a wide range of drive functions, for example for driving compressors. Synchronous motors are advantageous to drive high-speed compressors. Synchronous motors are preferably in the form of two-pole, laminated or solid, solid-pole rotors or turbo-rotors.
The electrical machines mentioned above are preferably fed via one or more parallel-connected converters. In particular, the converter is a voltage intermediate-circuit converter for producing a three-phase or polyphase output voltage. The conversion is carried out via a voltage intermediate circuit with an energy storage capacitor. On the output side, the voltage intermediate circuit feeds a pulse-controlled inverter as part of the converter.
In certain fields of application, electrical drive redundancy may be required or even absolutely essential. In the case of an electrical drive of the type mentioned above, it is in principle possible to design the converters and/or the electrical machine redundantly. In the case of two-pole synchronous motors which are operated from a current intermediate-circuit converter, one known measure is to provide two winding systems or three-phase windings which are pivoted through 30° with respect to one another. The two winding systems are each fed from one converter.
By way of example, redundancy can be achieved on the converter side by providing a third converter which can replace a failed converter. Alternatively, the rating when there are only two converters may be designed such that, if one converter fails, the remaining converter can take over the entire feed required. A converter which is redundant in this way may be designed to be appropriately powerful. The expression “rating” normally relates to the maximum electrical power consumed during continuous operation.
If, in contrast, one of the winding systems on the motor side fails, for example as a result of a short, then only half the rating or half the torque of the electrical machine is then available, irrespective of the converter-side design.
In order to achieve converter-side and motor-side redundancy, it is disadvantageously necessary to design an electrical machine such as this from the rating point of view such that, if one of the two at least three-phase winding systems fails, the other winding system can carry all of the current for the full torque. In consequence, the electrical machine must be greatly over designed, with each of the winding systems carrying only half the maximum current during normal operation.